1. Field of the Invention
The present invention relates to a device for use in fixing an element to a panel of hollow or sandwich construction by means of a fastening member, such as a screw or a pin or the like, which passes through the panel, said panel comprising two parallel skins which are spaced from each other and are provided with two aligned holes, one through each skin, through which the fastening member passes.
Box structures or sandwich-type panels to which it is necessary to fix elements firmly by screwing, pose fixing problems associated with the absence of material in the region between the two skins of such structures. Even if the element to be fixed to these structures has a surface wide enough to provide a bearing which avoids depression of the first skin in contact with the element, this does not apply to the second skin in contact with the screw fastener which, on tightening, will cause deformation of the skin, thus preventing achievement of a proper fastening. Furthermore, if the surface of the element bearing on the first skin is small, then both skins will be deformed. Accordingly, it is imperative to find a fixing device which enables a proper fastening for this type of structure to be achieved without undue deformation of the skins around the holes and without crushing the panel.
2. Summary of the Prior Art
It has already been proposed to use an annular spacer in such a manner that the axial faces of the spacer bear against the inner faces of the skins around the holes or are situated in the holes to operate directly as bearing surfaces for the fastening member and the element to be secured to the panel.
British Pat. No. 1296758 relates to a device comprising an annular spacer and two bushes sliding one inside the other and in the bore of the spacer, each bush comprising a flange surrounding the hole in the corresponding skin and engaging the outer face of this skin. The two holes in the skins have different sizes to permit the insertion of the spacer through the larger hole. The bushes have outer walls of conical shape which widen the ends of the spacer so that they come to be positioned at the periphery of the holes and near the inner faces of the skins. Also, the flanges have inner walls of conical shape intended to deform the periphery of the holes when the device is assembled, so that this periphery may adopt a conical shape and be interposed between the end face of the spacer and the inner face of the flange. This deformation of the periphery of the holes may cause a tearing of the skin in the vicinity of the holes, which is detrimental to the quality of the fastening. Moreover, the device involves three different parts with shapes matched in pairs and accurately formed so as to allow correct deformation of the spacer and the securing of the two bushes together after the device has been mounted in position.
French Patent Application No. FR-A-2 440 485 discloses a fixing device for a honeycomb panel wherein the axial faces of the spacer do not act on the inner faces of the skins. The spacer is held in place by two thin plates each provided with a hole having its edge adapted to the corresponding end of the spacer, the said plates being fixed by adhesive on the outer faces of the skins. In this arrangement nothing prevents a crushing or coming closer together of the skins in the vicinity of the holes.
French Patent Application FR-A-2 256 687 also relates to a fixing device for a panel of sandwich construction, the device comprising a spacer of cylindrical form which is inserted between the skins through a larger size hole in one of the skins, and the end faces of which come to act against the inner faces of the skins as a consequence of deformation of the spacer under the action of a pin or rivet fitted with a cylindrical portion designed to expand the spacer. This arrangement requires riveting means for it to be used.